Cutting tools such as cutting inserts, milling tools, drilling tools etc. may be used for chip forming machining of material, such as metals. Such tools are most often made of a durable material such as cemented carbide, cubic boron nitride or high speed steel. To improve the properties of the tool, e.g. wear properties, such tools are commonly provided with a surface coating. Such coatings may be deposited on the tool by means of chemical (CVD) or physical (PVD) vapour deposition.
Different types of surface coatings have been used until now, e.g. TiN, TiAlN. During metal machining with a coated cutting tool, the temperature in the vicinity of the cutting edge of the tool will increase due to shearing of the machined material, and friction. The temperature may thus become very high at the coating, i.e. 1100° C. or more. Cubic TiAlN normally decomposes into cubic TiN and cubic AlN at 800-900° C., and thereafter the cubic AlN transforms into hexagonal wurtzite AlN at about 1000° C., which is a less desirable phase. In EP 2628826 A1 a multilayer coating of alternating layers of ZrAlN and TiN is disclosed. This type of coating was developed to provide a high thermal stability of the coating in order to provide a high hardness even if subjected to such high temperatures.
It is sought to further develop surface coatings with improved properties when subjected to high temperatures. In particular, it is desirable to provide coatings having a low likelihood of decomposing into less desirable phases at elevated temperatures, e.g. hexagonal AlN phases. Therefore, it is sought to provide a coated cutting tool with a coating having a composition which is relatively stable at elevated temperatures.